Colombo (Sinhala: කොළඹ, romanized: Koḷam̆ba, IPA: [ˈkoləmbə]; Tamil: கொழும்பு, romanized: Koḻumpu, IPA: [koɻumbɯ]) is the commercial capital and largest city of Sri Lanka by population. According to the Brookings Institution, Colombo metropolitan area has a population of 5.6 million, and 752,993 in the Municipality. It is the financial centre of the island and a tourist destination. It is located on the west coast of the island and adjacent to the Greater Colombo area which includes Sri Jayawardenepura Kotte, the legislative capital of Sri Lanka, and Dehiwala-Mount Lavinia. Colombo is often referred to as the capital since Sri Jayawardenepura Kotte is itself within the urban/suburban area of Colombo. It is also the administrative capital of the Western Province and the district capital of Colombo District. Colombo is a busy and vibrant city with a mixture of modern life, colonial buildings and monuments.Due to its large harbour and its strategic position along the East–West sea trade routes, Colombo was known to ancient traders 2,000 years ago. It was made the capital of the island when Sri Lanka was ceded to the British Empire in 1815, and its status as capital was retained when the nation became independent in 1948. In 1978, when administrative functions were moved to Sri Jayawardenepura Kotte, Colombo was designated as the commercial capital of Sri Lanka.

Like many cities, Colombo's urban area extends well beyond the boundaries of a single local authority, encompassing other municipal and urban councils such as Sri Jayawardenepura Kotte Municipal Council, Dehiwala Mount Lavinia Municipal Council, Kolonnawa Urban Council, Kaduwela Municipal Council, and Kotikawatte Mulleriyawa Pradeshiya Sabha. The main city is home to a majority of Sri Lanka's corporate offices, restaurants, and entertainment venues. Famous landmarks in Colombo include Galle Face Green, Viharamahadevi Park, Beira Lake, Colombo Racecourse, Planetarium, University of Colombo, Mount Lavinia beach, Dehiwala Zoological Garden, Nelum Pokuna Theatre, One Galle Face, Gangaramaya Temple, Dutch Museum, Colombo Lotus Tower as well as the National Museum.